Five-axis iso-error numerical control tool path generation for flat-end tool machining sculptured surface

The quality of numerical control (NC) tool path directly affects the machining precision and efficiency. As a basic parameter of tool path generation, step error represents the difference between tool path and machined surface, which is closely relevant to the distance (named step length) between adjacent cutter contacting (CC) points along feed direction. The step error along feed direction in machining process is actually the maximum error between tool envelope surface and CC curve. Ideally, step error is expected equal to the maximum allowable value so as to obtain theoretical maximum step length and least CC points. For this purpose, this paper presents a method of iso-error tool path generation for five-axis sculptured surface machining with flat-end tool. Tool envelope surface of flat-end tool is irregular and hard to represent exactly because of rotational axes. Discrete bottom circles of flat-end tool are used to replace tool envelope surface and calculate step error iteratively. A step error calculation algorithm of a tool location is presented to calculate the minimum distance between a tool bottom circle and CC curve, and used to obtain the point on CC curve with maximum non-linear error. Another step error calculation algorithm of a point on CC curve is presented to search the maximum step error between the two points corresponding to the maximums of linear and non-linear errors. The maximum step error is the real step error between two adjacent CC points. Finally, as step length, the parameter increment between adjacent CC points is adjusted to make step error in the defined range, and iso-error CC points are obtained to generate iso-error tool path. Two step error calculation algorithms are major innovations in this paper. A typical free-form surface and a blade are taken as examples to generate tool path. Compared with the other methods, the presented method can generate tool path with uniform step error and much less CC points.